CN111655756B - Polymer composition for selective sintering - Google Patents
Polymer composition for selective sintering Download PDFInfo
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- CN111655756B CN111655756B CN201880086726.8A CN201880086726A CN111655756B CN 111655756 B CN111655756 B CN 111655756B CN 201880086726 A CN201880086726 A CN 201880086726A CN 111655756 B CN111655756 B CN 111655756B
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
- C08G63/88—Post-polymerisation treatment
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
- B29C64/00—Additive manufacturing, i.e. manufacturing of three-dimensional [3D] objects by additive deposition, additive agglomeration or additive layering, e.g. by 3D printing, stereolithography or selective laser sintering
- B29C64/10—Processes of additive manufacturing
- B29C64/141—Processes of additive manufacturing using only solid materials
- B29C64/153—Processes of additive manufacturing using only solid materials using layers of powder being selectively joined, e.g. by selective laser sintering or melting
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B33—ADDITIVE MANUFACTURING TECHNOLOGY
- B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
- B33Y10/00—Processes of additive manufacturing
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B33—ADDITIVE MANUFACTURING TECHNOLOGY
- B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
- B33Y70/00—Materials specially adapted for additive manufacturing
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- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
- C08G63/02—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds
- C08G63/12—Polyesters derived from hydroxycarboxylic acids or from polycarboxylic acids and polyhydroxy compounds derived from polycarboxylic acids and polyhydroxy compounds
- C08G63/16—Dicarboxylic acids and dihydroxy compounds
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- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
- C08K3/00—Use of inorganic substances as compounding ingredients
- C08K3/01—Use of inorganic substances as compounding ingredients characterized by their specific function
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
- B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
- B29K2067/00—Use of polyesters or derivatives thereof, as moulding material
- B29K2067/003—PET, i.e. poylethylene terephthalate
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Abstract
The invention relates to a polymer composition for producing shaped objects by selective sintering, wherein the polymer composition comprises a thermoplastic polyester selected from the group consisting of polyethylene terephthalate, polyethylene naphthalate, polyethylene furandicarboxylate, polypropylene terephthalate, polyethylene succinate or polyhydroxybutyrate, wherein more than or equal to 10.0 wt.% of the thermoplastic polyester is subjected to a heat treatment. Such polymer compositions allow the production of articles with continuous use temperatures ≡100 ℃ and result in low molecular weight changes during exposure to the processing temperatures of the selectively sintered powders. Furthermore, such a polymer composition results in a significant reduction in scrap generated during selective sintering, as unsintered material does not have to be discarded as waste, but can be reused entirely in another selective sintering process, or blended and reused with virgin material of the polymer composition.
Description
The present invention relates to a polymer composition for selective sintering. The invention also relates to a method for producing shaped objects by selective sintering using the polymer composition according to the invention. The invention further relates to shaped objects produced via selective sintering using the polymer composition according to the invention.
Selective sintering is an emerging technology that allows the production of complex three-dimensional objects. Currently, one of the main manufacturing techniques for such three-dimensional objects is via injection molding. Injection molding, however, involves the use of expensive molds, and thus injection molding is an efficient manufacturing technique only when the amount of objects produced using the molds is sufficiently large. Production costs are too high for producing smaller series of objects. Thus, alternative manufacturing techniques are needed that avoid the need to use such expensive molds.
One such alternative manufacturing technique is 3D printing. 3D printing is an additive manufacturing method that allows manufacturing of articles without using such expensive molds. Using Computer Aided Design (CAD), a model of the object to be produced is stored. Using such CAD models, a computer can manipulate a printing device by means of which a material can be shaped into a desired object. 3D printing may also allow for the production of articles having such complex shapes that may not be possible via injection molding.
The material used for 3D printing may be, for example, a thermoplastic material. In this case, the printing may be performed by subjecting predetermined portions of the thermoplastic material, for example a powdered thermoplastic material, to a radiation source, thereby ensuring that certain portions of the thermoplastic material reach a condition in which they sinter with adjacent portions of the material. Irradiation may be performed by exposing the thermoplastic material to electromagnetic radiation, such as infrared or near infrared radiation. Such irradiation may be carried out, for example, using radiation having a wavelength of 100nm or more and 100 μm or less, preferably 500nm or more and 15 μm or less, more preferably 700nm or more and 5 μm or less. Such methods are known as selective sintering methods.
In such selective sintering processes, irradiation may be performed, for example, using infrared or near infrared curing lamps, infrared or near infrared light emitting diodes, or laser sources. Such irradiation may be performed, for example, using laser irradiation.
The selective sintering process may, for example, include a process in which only selected portions of the material are subjected to radiation; alternatively, selective sintering may be achieved by applying a layer of radiation absorbing material to the region of the thermoplastic material to be sintered, and subsequently subjecting the surface region of the thermoplastic material, including the region to which the radiation absorbing material is not applied, to a radiation source. Such selective sintering processes include, for example, high Speed Sintering (HSS) processes.
Selective sintering processes in which only selected portions of the material are subjected to radiation include, for example, processes that can be irradiated, for example, using laser irradiation. One technique for laser irradiation sintering of predetermined portions of a material, such as a thermoplastic material, is Selective Laser Sintering (SLS). In SLS, a powder, such as a powdered thermoplastic, is located on a bed where a laser source irradiates those portions of the powdered thermoplastic on the bed as indicated by a CAD model in such a way as to melt the thermoplastic material in that region. The molten material may then adhere to the underlying thermoplastic material. Such an underlayer may be a layer formed in advance by the SLS method. In this way, the desired object can be produced layer by layer. The unsintered powder material may be removed, for example by dusting, and may be reused in a subsequent SLS process.
Thus, objects produced using a selective sintering process such as the SLS process are cost-effectively produced. However, not every thermoplastic material is suitable for producing objects via SLS. Problems such as object curling, orange peel, undesirable surface roughness, or fuming often occur during this process.
For example, when amorphous polymers are used to produce objects via the SLS process, this can result in objects of insufficient quality. This can be interpreted as amorphous polymers do not have a well-defined melting point, but rather soften over a wide temperature range and generally have a high viscosity. This can result in objects with undesirably high porosity and rough surfaces. Furthermore, individual particles may still be discernable. When higher irradiation intensities are used to overcome high viscosities, this may again lead to charring, or heat conduction such that the material in the unwanted areas softens, so the shape of the resulting object will not reflect the desired shape at the desired resolution.
On the other hand, highly crystalline polymers tend to melt at a well-defined melting point, absorbing the energy of the irradiation source to melt the crystallites without transferring the energy to the surrounding area to an undesirably large extent. However, highly crystalline polymers tend to have a fast crystallization rate, so that shrinkage and warpage of the formed object may result. This can be overcome by very gentle and slow cooling of the material after irradiation; however, this then leads to an undesirable increase in the time required for the SLS process.
In the SLS process according to the prior art polylaurolactam, also known as nylon-12, is often used as thermoplastic material. However, nylon-12 has the disadvantage of having a low melting point of 175 ℃, which results in the limitation of continuous use temperatures of the shaped object below 100 ℃. For some applications, continuous use temperatures above 100 ℃ are required. More preferably, the material can withstand temperatures above 200 ℃ for a short period of time without losing its desired properties.
Thus, there is a need to develop thermoplastic materials suitable for selective sintering that can be used in the production of shaped objects requiring a continuous use temperature of ≡100 ℃. The continuous use temperature can be determined, for example, in the case of amorphous thermoplastic polymers at the glass transition temperature (T g ) Is defined; alternatively, in the case of crystalline polymers, it can be defined as being below the peak melting temperature (T m )30℃。
Another disadvantage of nylon-12 is that the material is vulnerable to changes in properties due to temperature exposure. This results in limited re-use capabilities of the remainder of the SLS process, which has not been melted or sintered by selective irradiation, but has been exposed to heat for long periods of time during the pre-heating, build and cooling stages. Exposure to powder bed temperature during SLS resulted in a weight average molecular weight M of nylon-12 w Variations, in turn, negatively affect several material properties, including melt viscosity.
Furthermore, when nylon-12 is used, only a small portion of the powder introduced to the selective sintering process may be formed from material that has been subjected to such a sintering process (i.e., only a small amount of unsintered material from the previous construction may be used). During the selective sintering process, a powder bed is formed from the material at an elevated temperature, but below the melting temperature of the material. Because only a certain portion of the powder material is produced as a melted or sintered material forming the shaped object, a certain portion, typically even a significant portion, of the material remains in powder form. But such powders are subjected to thermal exposure in the powder bed. For thermoplastic powders in the art, such as nylon-12 powders, this temperature exposure causes some change in the material, so they become unsuitable for reuse in additional selective sintering processes, and thus may need to be discarded as scrap, or at best can be used only as a smaller portion of the powder used in additional selective sintering processes, with the major portion consisting of virgin material. This obviously results in inefficiency of the process, increased costs and the appearance of unwanted waste streams.
One class of thermoplastic materials known to have high melting points and high continuous use temperatures are certain thermoplastic polyesters, such as semi-aromatic thermoplastic polyesters. For example, US20140221566A1 describes the use of a specific type of thermoplastic polyester, polybutylene terephthalate (PBT), in SLS processing. The disadvantage of PBT is its fast crystallization rate, which can lead to curling and slow down the rate of structuring of the resulting product.
Thermoplastic polyesters for use in SLS processing are also described in US20070126159 A1. However, the polyesters disclosed in this publication, which are prepared by polycondensation of di-or polyhydric aliphatic alcohols and aliphatic dicarboxylic acids, do not have the desired high melting point and therefore do not have the desired continuous use temperature of ≡100 ℃.
Thus, the foregoing clearly presents the need to provide thermoplastic materials that have a continuous use temperature of ≡100 ℃ and that exhibit low molecular weight changes during exposure to SLS powder processing temperatures. Furthermore, it is desirable that the articles produced via SLS are crystalline rather than amorphous. In particular, it is desirable that the material can be utilized in such a way that the amount of waste material after the sintering process is reduced. Waste herein may be understood as a material that is not suitable for use in the selective sinter forming process.
This has now been achieved according to the invention by a polymer composition for the production of shaped objects via selective sintering, wherein the polymer composition comprises a thermoplastic polyester selected from the group consisting of polyethylene terephthalate, polyethylene naphthalate, polyethylene furandicarboxylate, polypropylene terephthalate, polyethylene succinate or polyhydroxybutyrate, wherein > 10.0% by weight of the thermoplastic polyester is subjected to a heat treatment.
Such polymer compositions allow the production of articles with continuous use temperatures ≡100 ℃ and result in low molecular weight changes during exposure to the processing temperatures of the selectively sintered powders. Furthermore, such a polymer composition results in a significant reduction in scrap generated during selective sintering, as unsintered material does not have to be discarded as waste, but can be reused entirely in another selective sintering process, or blended with virgin material of the polymer composition and reused.
Preferably, greater than or equal to 25.0 wt.%, preferably greater than or equal to 50.0 wt.%, even more preferably greater than or equal to 75.0 wt.%, even more preferably 100.0 wt.% of the thermoplastic polyester has been heat treated, relative to the total weight of the thermoplastic polyester in the polymer composition.
For example, 10.0 and 90.0 wt.%, preferably 25.0 and 90.0 wt.%, more preferably 25.0 and 80.0 wt.%, even more preferably 50.0 and 80.0 wt.% or less of the thermoplastic polyester has been heat treated relative to the total weight of thermoplastic polyester in the polymer composition. Polymer compositions comprising such thermoplastic polyesters are understood to have a particularly desirable color appearance. It is also understood that the use of such thermoplastic polyesters allows materials that have been subjected to heat treatment for long durations to be utilized.
The use of such thermoplastic polyesters in polymer compositions that have been subjected to selective laser sintering, in particular in such amounts, allows for the desired reduction in the amount of polymer composition that must be discarded as unsintered material that is no longer suitable for use in a selective sintering forming operation after the selective sintering process, and still produce a formed object having the desired material properties from the selective sintering.
The heat treatment may, for example, comprise exposing the thermoplastic polyester to a temperature above the glass transition temperature T g More than 100 ℃ and less than the peak melting temperature T p,m Less than 10 ℃, preferably greater than T g More than 125 ℃ and less than T p.m A temperature of less than 20 ℃, wherein T g Determined according to ISO 11357-2 (2013) and T p,m Measured according to ISO 11357-3 (2011) first heat run.
The heat treatment may be, for example, exposing the powder material to an elevated powder bed temperature during the selective sintering process. The elevated powder bed temperature may be, for example, above the glass transition temperature T g More than 100 ℃ and less than the peak melting temperature T p,m Less than 10deg.C, preferably greater than T g More than 125 ℃ and less than T p.m A temperature of less than 20 ℃.
Preferably, the thermoplastic polyester that has been subjected to heat treatment is a thermoplastic polyester that has been produced as an unsintered material from a selective sintering process.
In the case where the thermoplastic polyester is polyethylene terephthalate, the temperature of the heat treatment may be, for example, 170℃or more and 230℃or less, preferably 200℃or more and 230℃or less. Particularly preferred thermoplastic polyesters are polyethylene terephthalates, very particularly preferred are polyethylene terephthalate homopolymers.
Preferably, the thermoplastic polyester which has been heat treated is a thermoplastic polyester which has been produced as an unsintered material from a selective sintering process in which the powder bed temperature is above the glass transition temperature T g More than 100 ℃ and less than the peak melting temperature T p,m Less than 10deg.C, preferably greater than T g More than 125 ℃ and less than T p.m A temperature of less than 20 ℃.
Particularly preferably, the thermoplastic polyester which has been subjected to a heat treatment is polyethylene terephthalate which has been produced as an unsintered material from a selective sintering process in which the powder bed temperature is above the glass transition temperature T g More than 100 ℃ and less than the peak melting temperature T p,m Less than 10deg.C, preferably greater than T g More than 125 ℃ and less than T p.m A temperature of less than 20 ℃.
It is further particularly preferred that the thermoplastic polyester which has been subjected to a heat treatment is polyethylene terephthalate which has been produced as an unsintered material from a selective sintering process in which the powder bed temperature is greater than or equal to 170℃and less than or equal to 230℃and preferably greater than or equal to 200℃and less than or equal to 230 ℃.
The heat treatment may, for example, have a duration of ≡1 hour. Preferably, the heat treatment has a duration of not less than 2 hours, more preferably not less than 5 hours and may even be at most 4 days.
The crystallinity of the thermoplastic polyesters is preferably ≡10.0%, more preferably ≡12.5%, even more preferably ≡15.0%, and especially ≡40.0%, as determined by the formula:
wherein:
d = crystallinity (%) of thermoplastic material;
·ΔH f melting enthalpy of thermoplastic material as determined according to ISO 11357-3 (2011);
·ΔH f,100 melting enthalpy of thermoplastic material in 100% crystalline state.
Preferably the thermoplastic polyester has such crystallinity. In the case of producing objects using a material having such crystallinity, the continuous use temperature can be understood to be related to the crystallization melting temperature and is thus desirably high; in the case of the production of objects using amorphous materials, the continuous use temperature is understood to be limited to the glass transition temperature.
Preferably, the polymer composition comprises greater than or equal to 70.0 wt.%, more preferably greater than or equal to 80.0 wt.%, even more preferably greater than or equal to 90.0 wt.%, even more preferably greater than or equal to 95.0 wt.%, relative to the total weight of the polymer composition, of a thermoplastic polyester.
It is particularly preferred that the polymer composition comprises not less than 70.0 wt.%, more preferably not less than 80.0 wt.%, even more preferably not less than 90.0 wt.%, even more preferably not less than 95.0 wt.%, relative to the total weight of the polymer composition, of a thermoplastic polyester, wherein the thermoplastic material is a polyester selected from the group consisting of polyethylene terephthalate, polyethylene naphthalate, polyethylene furandicarboxylate, polypropylene terephthalate, polyethylene succinate and polyhydroxybutyrate.
It is even more particularly preferred that the polymer composition comprises not less than 70.0 wt.%, more preferably not less than 80.0 wt.%, even more preferably not less than 90.0 wt.%, even more preferably not less than 95.0 wt.%, relative to the total weight of the polymer composition, of a thermoplastic polyester, wherein the thermoplastic material is a polyester, which is polyethylene terephthalate.
Further specifically, it is preferred that the polymer composition comprises not less than 70.0 wt.%, more preferably not less than 80.0 wt.%, even more preferably not less than 90.0 wt.%, even more preferably not less than 95.0 wt.%, relative to the total weight of the polymer composition, of a thermoplastic polyester, wherein the thermoplastic polyester is a polyester selected from the group consisting of polyethylene terephthalate, polyethylene naphthalate, polyethylene furandicarboxylate, polypropylene terephthalate, polyethylene succinate or polyhydroxybutyrate, and wherein not less than 10.0 wt.%, relative to the total weight of the thermoplastic polyester in the polymer composition, of the thermoplastic polyester has been subjected to a selective sintering process.
Even further specifically, it is preferred that the polymer composition comprises not less than 70.0 wt.%, more preferably not less than 80.0 wt.%, even more preferably not less than 90.0 wt.%, even more preferably not less than 95.0 wt.%, relative to the total weight of the polymer composition, of a thermoplastic polyester, wherein the thermoplastic polyester is polyethylene terephthalate, and wherein not less than 10.0 wt.%, preferably not less than 25.0 wt.%, more preferably not less than 50.0 wt.%, even more preferably not less than 75.0 wt.%, relative to the total weight of the thermoplastic material in the polymer composition, of the thermoplastic polyester is a thermoplastic polyester that has been produced as an unsintered material from a selective sintering process.
Preferably the polymer composition is a powder having an average particle volume size of ≡10 and ≡300 μm, more preferably ≡50 and ≡250 μm or ≡100 and ≡200 μm as determined according to ISO 9276-2 (2014). Such powders are particularly suitable for processing via SLS sintering, allowing the production of objects with low porosity. It is further preferred that the polymer composition is a polymer having a D of.gtoreq.5 and.ltoreq.50 μm as determined according to ISO 9276-2 (2014) 10 D of 60 or more and 150 μm or less 50 And D of 160 μm or more and 300 μm or less 90 Is a powder of (2); more preferably, the powder has a D of 10 μm or more and 40 μm or less 10 D of equal to or more than 75 and equal to or less than 100 mu m 50 And D of 160 μm or more and 200 μm or less 90 . Polymer compositions having such particle size distribution are particularly suitable for processing via SLS because they allow good material flow during filling of the powder bed, combined with good shape stability of the powder bed. Furthermore, if the particles are too large, sintering of the material will be insufficient after exposure to SLS. If the particles are too fine, it may become difficult to form a powder layer on the build area.
A particularly preferred embodiment of the invention relates to a polymer composition comprising not less than 70.0 wt.%, more preferably not less than 80.0 wt.%, even more preferably not less than 90.0 wt.%, even more preferably not less than 95.0 wt.% of a thermoplastic material, relative to the total weight of the polymer composition, wherein the thermoplastic material is a polyester, is polyethylene terephthalate, and wherein not less than 10.0 wt.%, preferably not less than 25.0 wt.%, even more preferably not less than 50.0 wt.% of the thermoplastic polyester, relative to the total weight of the thermoplastic polyester in the polymer composition, is a thermoplastic polyester that has been produced as a green material from a selective sintering process, wherein the polymer composition is a powder having an average particle volume size of not less than 10 and not more than 300 μm, as determined according to ISO 9276-2 (2014).
The change in molecular weight can be determined, for example, via gel permeation chromatography, for example according to ISO 16014-1 (2012), whereby a molecular weight such as weight average molecular weight (M w ) Number average molecular weight (M) n ) Is a parameter of (a). Alternatively, the change in molecular weight may be determined by dilute solution viscometry, for example according to ASTM D2857-95 (2007), whereby Intrinsic Viscosity (IV) is obtained. The change in molecular weight can be expressed as M measured before and after exposure of the polymer composition to SLS powder bed temperature w 、M n And/or IV differences.
The DSC curve of the polymer composition is preferably obtained at a heating and cooling rate of 10℃per minute. In a preferred assay format, the sample is first heated to obtain a melting peak via DSC, wherein with an increase in temperature, a melting start temperature is first obtained, followed by a melting peak temperature, and then a melting end temperature according to the definition of ISO11357-1 (2009); during subsequent cooling, the crystallization end temperature is obtained first, followed by the crystallization peak temperature, and then the crystallization start temperature, according to the definition of ISO11357-1 (2009).
Furthermore, the thermoplastic polyesters may, for example, have a glass transition temperature T of ≡50 ℃, preferably ≡60 ℃, more preferably ≡70 ℃ as determined according to ISO 11357-2 (2013) g 。
The thermoplastic polyesters may, for example, have a peak melting temperature T of 200℃or more, preferably 220℃or more, more preferably 240℃or more, as determined according to ISO 11357-3 (2011) first heat run p,m 。
In the case of polyethylene terephthalate used in the polymer composition according to the invention, it is preferred that the polyethylene terephthalate has an intrinsic viscosity of not less than 0.80dl/g, more preferably not less than 1.00dl/g, even more preferably not less than 1.10 dl/g. It is also preferred that the polyethylene terephthalate has an intrinsic viscosity of 2.50dl/g or less, more preferably 2.00dl/g or less, still more preferably 1.50dl/g or less. For example, the polyethylene terephthalate may have an intrinsic viscosity of 0.80dl/g or more and 2.50dl/g or less, or 1.00dl/g or more and 1.50dl/g or less.
Intrinsic Viscosity (IV) is determined according to ASTM D2857-95 (2007).
Polyethylene terephthalate with such an inherent viscosity can exhibit a good combination of melt flow and strength of the sintered object after laser irradiation, and can produce an object with a desired dimensional accuracy.
It is particularly desirable to use polyethylene terephthalate having an intrinsic viscosity of not less than 0.80dl/g and not more than 2.50dl/g and a crystallinity of not less than 15.0%, preferably not less than 40.0%. Such polyethylene terephthalate exhibits a very desirable resistance to changes in molecular weight over prolonged heat treatment and is therefore most suitable for reuse in such processes when obtained as unsintered material from a selective sintering process.
It is also particularly desirable to use polyethylene terephthalate having a heat of fusion of > 50J/g.
The polymer composition according to the invention may for example comprise polyethylene terephthalate. For example, the polymer composition may comprise greater than or equal to 80.0 wt.%, or greater than or equal to 90 wt.%, or greater than or equal to 95.0 wt.% polyethylene terephthalate, relative to the total weight of the polymer composition. The polyethylene terephthalate may be a homopolymer or a copolymer. If the polyethylene terephthalate is a copolymer, the polyethylene terephthalate may, for example, comprise less than or equal to 15.0 wt.%, or less than or equal to 10.0 wt.%, or less than or equal to 5.0 wt.%, or less than or equal to 2.0 wt.% of units derived from the comonomer, relative to the total weight of the polyethylene terephthalate. Preferably, the polyethylene terephthalate comprises greater than or equal to 0.1 wt.% and less than or equal to 10.0 wt.%, or greater than or equal to 0.5 wt.% and less than or equal to 5.0 wt.% of units derived from the comonomer, relative to the total weight of the polyethylene terephthalate. The units derived from the comonomer may be, for example, units derived from aliphatic diols other than ethylene glycol. The units derived from the comonomer may be, for example, units derived from aromatic dicarboxylic acids other than terephthalic acid. For example, the aromatic dicarboxylic acid other than terephthalic acid may be isophthalic acid. Preferably, in the case where the polyethylene terephthalate is a copolymer, it comprises not less than 0.5% by weight and not more than 5.0% by weight of units derived from isophthalic acid relative to the total weight of the polyethylene terephthalate.
In a preferred embodiment of the invention, the polyethylene terephthalate has an intrinsic viscosity of not less than 1.00dl/g and not more than 1.50 dl/g.
In certain embodiments, the polymer composition may further comprise a flow agent. For example, the polymer composition may comprise ≡0.01% by weight and ≡5.00% by weight of the flow agent relative to the total weight of the polymer composition. Alternatively, the polymer composition may comprise greater than or equal to 0.05 and less than or equal to 3.00 wt%, or greater than or equal to 0.10 and less than or equal to 1.50 wt% of the flow agent, based on the total weight of the polymer composition. The flow agent may be selected, for example, from silica, alumina, phosphate, borate, titanium dioxide, talc, mica, kaolin, attapulgite, calcium silicate, magnesium silicate, or combinations thereof. For example, the polymer composition may comprise ≡0.01% by weight and ≡5.00% by weight, relative to the total weight of the polymer composition, of a flow agent selected from silica, alumina, phosphate, borate, titania, talc, mica, kaolin, attapulgite, calcium silicate, magnesium silicate or a combination thereof.
In another embodiment, the present invention also relates to a method for producing a shaped object using the polymer composition according to the present invention, wherein the method comprises the steps of:
(a) Providing an amount of a powder comprising a polymer composition;
(b) Irradiating a portion of the polymer composition with an irradiation source such that particles in the portion of the polymer composition absorb sufficient heat to reach a temperature above T p,m Is set at a temperature of (2);
(c) Terminating the portion of the polymer compositionExposure to a radiation source to reduce the temperature of the particles of the polymer composition to below T p,m The method comprises the steps of carrying out a first treatment on the surface of the And
(d) Removing portions of the polymer composition that have not been sintered by irradiation with an energy source;
wherein steps (a) through (d) are performed in this order.
In yet another embodiment, the present invention also relates to a method for producing a shaped object using the polymer composition according to the present invention, wherein the method comprises the steps of:
(a) Providing an amount of a powder comprising a polymer composition;
(b) Irradiating a portion of the polymer composition with an irradiation source such that particles in the portion of the polymer composition absorb sufficient heat to reach a temperature above T p,m Is set at a temperature of (2);
(c) Terminating exposure of the portion of the polymer composition to the irradiation source such that the temperature of the particles of the polymer composition is reduced to less than T p,m The method comprises the steps of carrying out a first treatment on the surface of the And
(d) Removing portions of the polymer composition that have not been sintered by irradiation with an energy source;
wherein steps (a) through (d) are performed in this order;
wherein the portion of the polymer composition removed in step (d) is further used in the polymer composition for use in an additional forming process according to steps (a) - (d).
In yet another embodiment, the present invention also relates to a method for producing a shaped object using the polymer composition according to the present invention, wherein the method comprises the steps of:
(a) Providing an amount of a powder comprising a polymer composition, wherein a portion of the polymer composition has been previously subjected to selective sintering;
(b) Irradiating a portion of the polymer composition with an irradiation source such that particles in the portion of the polymer composition absorb sufficient heat to reach a temperature above T p,m Is set at a temperature of (2);
(c) Terminating exposure of the portion of the polymer composition to the irradiation source such that the polymer compositionThe temperature of the particles is reduced to below T p,m The method comprises the steps of carrying out a first treatment on the surface of the And
(d) Removing portions of the polymer composition that have not been sintered by irradiation with an energy source;
wherein steps (a) through (d) are performed in this order.
Preferably, the polymer composition provided in (a) above comprises ≡10.0 wt% of thermoplastic polyester which has been produced as unsintered material from a selective sintering process.
In a preferred embodiment of the present invention, in a preferred embodiment,
step (a) comprises placing an amount of powder comprising a polymer composition in a powder bed comprising a horizontal surface and a frame for holding the powder on the surface;
step (b) comprises irradiating the portion of the polymer composition with a mobile irradiation source; and
repeating steps (a), (b) and (c) in this order before performing step (d) to form stacked layers of polymer composition sintered to each other.
In particular, the invention also relates to a method for producing a shaped object using the polymer composition according to the invention, wherein the method comprises the steps of:
(a) Providing an amount of a powder comprising a polymer composition;
(b) Irradiating a portion of the polymer composition with a laser energy beam such that particles in the portion of the polymer composition absorb sufficient heat to reach a temperature above T p,m Is set at a temperature of (2);
(c) Terminating exposure of the portion of the polymer composition to irradiation by the laser energy beam to reduce the temperature of the particles of the polymer composition to below T p,m The method comprises the steps of carrying out a first treatment on the surface of the And
(d) Removing portions of the polymer composition that have not been sintered by irradiation with an energy source;
wherein steps (a) through (d) are performed in this order.
In a preferred embodiment of the present invention, in a preferred embodiment,
step (a) comprises placing an amount of powder comprising a polymer composition in a powder bed comprising a horizontal surface and a frame for holding the powder on the surface;
step (b) comprises irradiating the portion of the polymer composition by moving the beam of laser energy; and
repeating steps (a), (b) and (c) in this order before performing step (d) to form stacked layers of polymer composition sintered to each other.
The process is preferably carried out in an atmosphere comprising +.1.0 wt.% oxygen.
The thermoplastic material in the powder bed subjected to irradiation is typically preheated to a temperature that minimizes the irradiation energy and time required for softening the material for sintering, while the material remains in a state where the powder particles not subjected to irradiation are not sintered. If the powder bed temperature is too high, it can cause sintering of the thermoplastic material in undesired locations, resulting in dimensional inaccuracy of the shaped object, among other things. If the powder bed temperature is too low, the thermoplastic material may not sinter sufficiently in the desired locations, which may result in, inter alia, undesirable porosity of the shaped object. For example, the powder bed temperature may be maintained below T p,m 60 ℃ or less, more preferably 40 ℃ or less, even more preferably 10 ℃ or more and 60 ℃ or 20 ℃ or less and 40 ℃ or less.
In the method according to the invention, further additives which may contribute to the selective sintering process may be applied. For example, coalescing agents may be added. Such coalescing agents may, for example, comprise agents that enhance the absorption of electromagnetic radiation and convert the absorbed energy into thermal energy, thus facilitating the sintering process.
In a further embodiment, the invention relates to a shaped object produced via the process according to the invention, preferably wherein the shaped object has a porosity of 5.0% or less. More preferably, the shaped object has a porosity of 4.0% or less, or 3.0% or less. Density (ρ) of an article producible by SLS from a used material having the same composition and the same crystallinity SLS ) Density (. Rho.) with articles produced via injection molding IM ) A comparison was made to determine porosity. The porosity in% (P) can be calculated, for example, as:
the invention will now be illustrated by the following non-limiting examples.
Polyethylene terephthalate (PET) homopolymer powder having the following properties was used:
intrinsic Viscosity (IV) of 1.12dl/g as determined according to ASTM D2857-95;
particle size distribution as determined according to ISO 9276-2 (2014): d (D) 10 ＝39μm；D 50 ＝94μm；D 90 =188 μm; average particle volume size = 107 μm;
a weight average molecular weight (M) of 117.1kg/mol as determined according to ISO 16014-1 (2012) w ) And a number average molecular weight (M) of 44.8kg/mol n ) And a polydispersity index M of 2.62 w /M n 。
PET is virgin PET, which is understood to mean that the PET has not been subjected to any heat treatment after PET production (such as in a selective sintering machine).
The PET powder material was divided into 5 sample portions, each subjected to a heat treatment according to table I below. The heat treatment simulates the level of heat exposed to unsintered material during selective sintering as conductive heat and radiant heating from, for example, an infrared lamp.
Table I: heat treatment conditions and molecular weight of PET powder
| Sample of | A | B | C | D | E |
| Heat treatment time | Without any means for | 24h | 48h | 72h | 96h |
| M w (kg/mol) | 117.1 | 113.9 | 118.8 | 125.5 | 130.0 |
| M n (kg/mol) | 44.8 | 44.2 | 46.3 | 47.3 | 49.1 |
| M w /M n | 2.62 | 2.58 | 2.56 | 2.65 | 2.65 |
The heat treatment was performed using an oven in which the powder samples were placed under vacuum at a temperature of 210 ℃ for a period of time as indicated in table I above. M of sample w And M n Each measured after heat treatment.
Sample a can be understood as a comparative example. Can be observed as by M w 、M n And M w /M n The molecular structure changes from that defined, but only to a very limited extent. The numerical difference is within the variance (±12%) of GPC measurements, and thus it can be inferred that there is no statistically significant difference. Surprisingly, and unlike other polymer powders for SLS, the heat treated materials of samples B to E still have a quality such that they can be used as sinterable materials during selective sintering, even without the need to add virgin PET powder.
Heat treated samples B-E, which may also be referred to as aged powder samples, and comparative sample a were subjected to Differential Scanning Calorimetry (DSC) according to ISO11357-1 (2009). The first melting curve and the first cooling curve were recorded at a heating and cooling rate of 10 ℃/min in a nitrogen atmosphere. From the DSC curve, the extrapolated melting onset temperature (T) of the first heat in degrees Celsius is determined ei,m ) Peak melting temperature at first heating (T p,m ) The extrapolated crystallization onset temperature (T) of the first heat in J/g ei,c ) Peak crystallization temperature in degrees centigrade (T p,c ) Heat of crystallization in J/g, and sintering window in c. The sintering window is calculated as T ei,m -T ei,c . The results are presented in table II.
Table II: DSC results
| Sample of | A | B | C | D | E |
| T ei,m | 238 | 238 | 239 | 238 | 239 |
| T p,m | 242 | 242 | 242 | 242 | 242 |
| Heat of fusion | 57.0 | 59.7 | 60.5 | 61.2 | 61.4 |
| T ei,c | 186 | 186 | 185 | 185 | 184 |
| T p,c | 175 | 176 | 175 | 173 | 173 |
| Heat of crystallization | 28.5 | 28.8 | 26.8 | 28.5 | 27.1 |
| Sintering window | 52 | 52 | 54 | 53 | 55 |
From the results in Table II, it can be further inferred that the suitability of samples B-E for use in the selective sintering process is not significantly affected by the heat treatment. For example, the sintering window increases even more, indicating that the temperature range to which the material is exposed during sintering becomes even less critical.
To further determine the properties of the sample materials and their suitability in the selective sintering process for producing objects with the desired properties, a certain amount of sample a and a certain amount of sample E, i.e. the material subjected to the most intense heat treatment, were each subjected to selective laser sintering to produce test bars 2cm wide, 5cm long and 3mm thick.
The use includes CO 2 The SLS machine of the laser source performs Selective Laser Sintering (SLS). To each of powder samples a and E was added Aerosil flow promoter in an amount of 0.05 wt%. The material is pre-dried prior to processing via SLS. The SLS process is carried out in an atmosphere having an oxygen content of 1.0 wt.%. The SLS process conditions are presented in table III.
Table III: SLS process conditions
| Powder bed temperature (. Degree. C.) | 228 |
| Piston temperature (. Degree. C.) | 180 |
| Barrel temperature (. Degree. C.) | 175 |
| Feed temperature (. Degree. C.) | 160 |
| Laser power (W) | 30 |
| Scanning speed (m/s) | 5 |
| Distance of hatch (mum) | 100 |
| Layer thickness (μm) | 100 |
The resulting rods were subjected to a determination of the density and the colour in the form of a yellow index of the rods. In kg/m 3 Is measured according to ASTM D792 (2013), according to method a; yellowness Index (YI) is determined according to ASTM E313 (2010). The results are presented in table IV.
Table IV: test results of SLS stick
These results show that the density of the printed bars is relatively unaffected by the use of virgin or heat treated materials.
Regarding the yellowness index, the results indicate that the YI of the rod produced using the heat treated material is even better than the YI of the rod produced using the neat material, indicating that the use of such heat treated material results in the desired color of the produced object.
Claims (16)
1. A process for producing a shaped object using a polymer composition comprising a thermoplastic polyester selected from the group consisting of polyethylene terephthalate, polyethylene naphthalate, polyethylene furandicarboxylate, polytrimethylene terephthalate, polyethylene succinate or polyhydroxybutyrate, wherein > 10.0% by weight of the thermoplastic polyester is subjected to a heat treatment,
wherein the method comprises the steps of:
(a) Providing an amount of a powder comprising the polymer composition, wherein a portion of the polymer composition has been previously subjected to selective sintering;
(b) Irradiating a portion of the polymer composition with a radiation source such that particles in the portion of the polymer composition absorb sufficient heat to reach a peak melting temperature T above that determined via DSC first heat run according to ISO11357-1 (2009) p,m Is set at a temperature of (2);
(c) Terminating exposure of said portion of said polymer composition to said irradiation source such that the temperature of said particles of said polymer composition is reduced to below T p,m The method comprises the steps of carrying out a first treatment on the surface of the And
(d) Removing portions of the polymer composition that have not been irradiated with an energy source;
wherein steps (a) through (d) are performed in this order; and
wherein the heat treatment comprises exposing the thermoplastic polyester to a temperature above the glass transition temperature T g More than 100 ℃ and less than the peak melting temperature T p,m A temperature of less than 10 ℃, wherein T g Determined according to ISO 11357-2 (2013) and T p,m First heat transport according to ISO 11357-3 (2011)Row to determine.
2. The method of claim 1, wherein the heat treatment is performed for 1 hour or more.
3. The method of any of claims 1-2, wherein the thermoplastic polyester is polyethylene terephthalate.
4. The method of claim 3, wherein the heat treating comprises exposing the polyethylene terephthalate to a temperature of ≡170 ℃ and ≡230 ℃.
5. The process of any of claims 1-2, wherein ≡75.0% by weight of the thermoplastic polyester is subjected to the heat treatment.
6. The method of any of claims 1-2, wherein the thermoplastic polyester subjected to the heat treatment is a thermoplastic polyester that results from a selective sintering process as an unsintered material.
7. The method of claim 3, wherein the polyethylene terephthalate is a polyethylene terephthalate homopolymer.
8. The method of claim 3, wherein the polyethylene terephthalate has an intrinsic viscosity of ≡0.80dl/g as determined according to ASTM D2857-95 (2007).
9. The method of claim 3, wherein the polymer composition comprises greater than or equal to 90.0 wt% of the polyethylene terephthalate relative to the total weight of the polymer composition.
10. The method of any of claims 1-2, wherein the polymer composition is a powder having an average particle volume size of ≡10 and ≡300 μιη as determined according to ISO 9276-2 (2014).
11. The method of any of claims 1-2, wherein the polymer composition is a polymer composition having a D of ≡5 and ≡50 μιη as determined according to ISO 9276-2 (2014) 10 D of 60 or more and 150 μm or less 50 And D of 160 μm or more and 300 μm or less 90 Is a powder of (a).
12. The method of any of claims 1-2, wherein the polymer composition further comprises ≡0.01% and ≡5.00% by weight of a flow agent selected from silica, alumina, phosphate, borate, titania, talc, mica, kaolin, attapulgite, calcium silicate, magnesium silicate, or combinations thereof, relative to the total weight of the polymer composition.
13. The method of any one of claims 1-2, wherein the radiation source is a laser energy beam.
14. Shaped object produced by the method according to any one of claims 1-13, wherein the shaped object has a porosity of ∈5.0%.
15. Use of a polymer composition comprising a thermoplastic polyester selected from the group consisting of polyethylene terephthalate, polyethylene naphthalate, polyethylene furandicarboxylate, polypropylene terephthalate, polyethylene succinate or polyhydroxybutyrate for reducing unsintered scrap polymer during selective sinter molding, wherein > 10.0 wt.% of the thermoplastic polyester is subjected to a heat treatment,
wherein the selective sinter molding process comprises steps (a) to (d) as defined in the method of claim 1, and
wherein the heat treatment comprises exposing the thermoplastic polyester to a temperature above the glass transition temperature T g More than 100 ℃ and less than the peak melting temperature T p,m A temperature of less than 10 ℃, wherein T g According to ISO 11357-2 (2013)Determination and T p,m Measured according to ISO 11357-3 (2011) first heat run.
16. The use according to claim 15, wherein the thermoplastic polyester subjected to the heat treatment is a thermoplastic polyester produced as an unsintered material from a selective sintering process.
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| EP17207825.5 | 2017-12-15 | ||
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| PCT/EP2018/084175 WO2019115455A1 (en) | 2017-12-15 | 2018-12-10 | Polymer composition for selective sintering |
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| US20220297376A1 (en) * | 2019-08-14 | 2022-09-22 | Solvay Specialty Polymers Usa, Llc | Additive manufacturing process for making a three-dimensional object using selective laser sintering |
| US20210245400A1 (en) * | 2020-02-10 | 2021-08-12 | 3Form, Llc | Architectural resin panel with incorporated scrap materials |
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| CN1105038A (en) * | 1993-12-28 | 1995-07-12 | 三井石油化学工业株式会社 | Process for preparing polyester |
| CN104169328A (en) * | 2011-12-12 | 2014-11-26 | 先进激光材料有限责任公司 | Method and system for laser sintering with pretreated material |
| CN105102199A (en) * | 2013-01-31 | 2015-11-25 | 沙特基础工业公司 | Process for making highly crystalline shaped part from PET or PEN |
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| US5527877A (en) | 1992-11-23 | 1996-06-18 | Dtm Corporation | Sinterable semi-crystalline powder and near-fully dense article formed therewith |
| US6110411A (en) | 1997-03-18 | 2000-08-29 | Clausen; Christian Henning | Laser sinterable thermoplastic powder |
| EP1413594A2 (en) * | 2002-10-17 | 2004-04-28 | Degussa AG | Laser-sintering powder with better recycling properties, process for its preparation and use thereof. |
| EP1598386B1 (en) * | 2003-02-28 | 2012-05-02 | Mitsubishi Chemical Corporation | Process for production of polyester resin powder, process for production of polyester preforms and thermal treatment equipment for polyester resin powder |
| DE102004001324A1 (en) * | 2003-07-25 | 2005-02-10 | Degussa Ag | Powder composition used in the layerwise buildup of three-dimensional articles comprises a polymer and an ammonium polyphosphate flame retardant |
| DE102004012682A1 (en) * | 2004-03-16 | 2005-10-06 | Degussa Ag | Process for the production of three-dimensional objects by means of laser technology and application of an absorber by inkjet method |
| DE102005054723A1 (en) | 2005-11-17 | 2007-05-24 | Degussa Gmbh | Use of polyester powder in a molding process and molding made from this polyester powder |
| US8247492B2 (en) | 2006-11-09 | 2012-08-21 | Valspar Sourcing, Inc. | Polyester powder compositions, methods and articles |
| DE102007024469B4 (en) | 2007-05-25 | 2009-04-23 | Eos Gmbh Electro Optical Systems | Method of layering a three-dimensional object |
| DE102012200160A1 (en) | 2012-01-06 | 2013-07-11 | Evonik Industries Ag | Device for the layered production of three-dimensional objects by means of a rotating application |
| US9925714B2 (en) | 2012-11-21 | 2018-03-27 | Stratasys, Inc. | Method for printing three-dimensional items wtih semi-crystalline build materials |
| EP3472222B1 (en) | 2016-06-20 | 2022-01-05 | SABIC Global Technologies B.V. | Polymer composition for selective sintering |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1105038A (en) * | 1993-12-28 | 1995-07-12 | 三井石油化学工业株式会社 | Process for preparing polyester |
| CN104169328A (en) * | 2011-12-12 | 2014-11-26 | 先进激光材料有限责任公司 | Method and system for laser sintering with pretreated material |
| CN105102199A (en) * | 2013-01-31 | 2015-11-25 | 沙特基础工业公司 | Process for making highly crystalline shaped part from PET or PEN |
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| CN111655756A (en) | 2020-09-11 |
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